4 Steps Visible Lock

This puzzle received the Grand Prize at the Puzzle Competition in 2011 which was held in Berlin. 

This puzzle is made out of Trespa which is a pressed wood material.  The top is made out of acrylic. 

The object of this puzzle seems easy enough.  Just remove the coin.  There are metal balls that will stop you from getting the coin out.   There is a catch to solving it which will be up to you to figure out. 

Due to this being a handmade puzzle, there may be imperfections.  The solution of the puzzle is still the same.